Hydraulic fluids are used in industrial machinery that perform work through the transfer of power from one location to another. Current hydraulic systems are often complicated, and involve motors, actuators, gear, vane, and piston pumps to convert hydraulic power into useful work. In addition to transferring power, hydraulic fluids must lubricate, transfer heat, and be compatible with other materials such as gaskets, seals, and metal components in the system.
While most commercially available hydraulic fluids are petroleum based, the increasingly important issues of environmental acceptance and biodegradability are drivers behind the desire for alternatives to petroleum based hydraulic fluids. It has been reported that over 60% of all lubricants end up in our soil and water, and such releases can cause contamination of the soil, ground, and surface water. A biodegradable option in hydraulic fluids are natural oil based polyol esters. Polyol esters are products of the transesterification of one or more fatty acids or fatty acid esters with one or more polyhydric alcohols. Such polyol esters are also lighter than water and not miscible with water, so they can be removed from wastewater streams via skimming.
One category of hydraulic fluids are fire-resistant hydraulic fluids. Fire-resistant hydraulic fluids must meet at least the following three fundamental requisites: (i) a high degree of flame propagation resistance; (ii) a lubricity adequate to the operating conditions existing in the hydraulic system; (iii) a high operational stability. Fire resistant hydraulic fluids containing polyol esters are categorized as Type HFDU, and generally have an operating range of −20° C. to 150° C.
Various biodegradable hydraulic fluids have been synthesized to address this concern. TMP oleate (trimethylolpropane trioleate) is considered an industry standard in formulating biodegradable hydraulic fluids. It has the appropriate viscosity (approximately 46 cSt at 40° C.) and biodegradability. However, polyunsaturated fatty acid components in natural oil-derived TMP oleate are readily susceptible to oxidative and thermal degradation which may impact service life and additive formulation requirements. Thus, there is interest in natural oil-based unsaturated polyol esters that lack polyunsaturated impurities, which may serve as effective, biodegradable alternatives to TMP oleate for fire-resistant hydraulic fluids.